rootdev: fix -d, add -c and -r. ifdefs for so use

Multiple changes:
- Ensure the -d flag trims off all of the partition info and only if there is a partition
- Add -c, device node creation for platform-agnostic /dev/ROOT, /dev/ROOT0 and /dev/ROOT1
- Add -r, resolve the first slave if the device is a device-mapper device
- Add -s, create a symlink from the found device to /dev/ACTIVE_ROOT
- Adds short-circuiting if /dev/ACTIVE_ROOT exists to both dm resolution and
  normal lookups
- Add support for building a library with a reusable header and interfaces

I'll follow this up with a change to install <rootdev/rootdev.h> and the .so in
the ebuild if the interface is at all interesting.  If prefered, I can just add:
rootdev -s -r to chromeos_startup, then AU can just rely on readlink(/dev/ACTIVE_ROOT).

BUG=chromium-os:5988
TEST=built for x86-generic testing with vroot: -r, -s, -c, -d and combos
     switching to non-vroot to test now
     can someone test arm for me?

Change-Id: Ibab8072afb012ea77d457517f1849e0917d02892

Review URL: http://codereview.chromium.org/3141038

9 files changed, 985 insertions, 446 deletions

diff --git a/COPYING b/COPYING
deleted file mode 100644
index 623b625..0000000
--- a/COPYING
+++ /dev/null
@@ -1,340 +0,0 @@
-		    GNU GENERAL PUBLIC LICENSE
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diff --git a/LICENCE b/LICENCE
deleted file mode 120000
index d24842f..0000000
--- a/LICENCE
+++ /dev/null
@@ -1 +0,0 @@
-COPYING
\ No newline at end of file
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..d251496
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,27 @@
+// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//    * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//    * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//    * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/Makefile b/Makefile
index 873a392..75d0702 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,19 @@
+# Copyright (C) 2010 The Chromium OS Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
 
-rootdev : rootdev.c
+all: rootdev librootdev.so.1.0
 
-.PHONY: clean clobber
-clean clobber:
-	rm -f rootdev
+rootdev: rootdev.c main.c
+	$(CC) $(CFLAGS) $(LDFLAGS) $^ -o $@ -O2 -Wall
+
+librootdev.so.1.0: rootdev.c
+	$(CC) $(CFLAGS) $(LDFLAGS) -shared -fPIC \
+          -Wl,-soname,librootdev.so.1 $< -o $@
+	ln -s $@ librootdev.so.1
+	ln -s $@ librootdev.so
+
+clean:
+	rm -f rootdev librootdev.so*
+
+.PHONY: clean
diff --git a/README.chromium b/README.chromium
index 5ed10c8..6e4e903 100644
--- a/README.chromium
+++ b/README.chromium
@@ -1,16 +1,15 @@
-URL: git://git.debian.org/~lamont/util-linux.git
-Version: commit 717db2c8177203fe242ea35b31bc312abe9aa3c9
-License: GPL v2
-License File: files/COPYING
-
-Description: Prints the current rootfs device.
-
-Local Modification:
-
-- Removed every bit of upstream code except the part that determines the
-  rootfs device.
-- Added better error messages.
+Chromium OS version of rootdev
 
+Inspired by git://git.debian.org/~lamont/util-linux.git / 717db2c8177203fe242ea35b31bc312abe9aa3c9
 
+Description: Performs operations to discover and annotate the root block device
 
+Prior to this commit, rootdev was derived from the above link.  However, it has
+been rewritten in its entirety and licensed as per LICENSE.
 
+chromeos-rootdev:
+- Provides core functionality in a library: librootdev
+- Walks sysfs to discover the block devices
+- Supports resolving through to /sys/block/XXX/slaves/*/dev devices
+- Will test and, optionally, symlink to the /dev entry for standard devices.
+- Is testable.
diff --git a/main.c b/main.c
new file mode 100644
index 0000000..61d20ca
--- /dev/null
+++ b/main.c
@@ -0,0 +1,157 @@
+/* Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ *
+ * Driver for using rootdev.c from the commandline
+ */
+#include <err.h>
+#include <errno.h>
+#include <getopt.h>
+#include <linux/limits.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "rootdev.h"
+
+static void print_help(const char *progname) {
+  fprintf(stderr,
+    "%s [OPTIONS] [PATH]\n"
+    "Outputs the containing device for the specified PATH.\n"
+    "With no arguments, '/' is assumed.\n"
+    "\n"
+    "Options:\n"
+    "  -h\tthis message.\n"
+    "\n"
+    "  -c\tcreate the /dev node if it cannot be found\n"
+    "  -d\treturn the block device only if possible\n"
+    "  -i\treturn path even if the node doesn't exist\n"
+    "  -s\tif possible, return the first slave of the root device\n"
+    "\n"
+    "  --block [path]\tset the path to block under the sys mount point\n"
+    "  --dev [path]\tset the path to dev mount point\n"
+    "  --major [num]\tset the major number of the rootdev\n"
+    "  --minor [num]\tset the minor number of the rootdev\n",
+    progname);
+}
+
+static int flag_help = 0;
+static int flag_use_slave = 0;
+static int flag_strip_partition = 0;
+static int flag_ignore = 0;
+static int flag_create = 0;
+static int flag_major = 0;
+static int flag_minor = 0;
+static const char *flag_path = "/";
+static char *flag_block_path = "/sys/block";
+static char *flag_dev_path = "/dev";
+
+static void parse_args(int argc, char **argv) {
+  while (1) {
+    int c;
+    int option_index = 0;
+    static const struct option long_options[] = {
+      {"c", no_argument, &flag_create, 1},
+      {"d", no_argument, &flag_strip_partition, 1},
+      {"h", no_argument, &flag_help, 1},
+      {"i", no_argument, &flag_ignore, 1},
+      {"s", no_argument, &flag_use_slave, 1},
+      /* Long arguments for testing. */
+      {"block", required_argument, NULL, 'b'},
+      {"dev", required_argument, NULL, 'd'},
+      {"major", required_argument, NULL, 'M'},
+      {"minor", required_argument, NULL, 'm'},
+      {0, 0, 0, 0}
+    };
+    c = getopt_long_only(argc, argv, "", long_options, &option_index);
+
+    if (c == -1)
+      break;
+
+    if (c == '?') {
+      flag_help = 1;
+      break;
+    }
+
+    switch (c) {
+    case 'b':
+      flag_block_path = optarg;
+      break;
+    case 'd':
+      flag_dev_path = optarg;
+      break;
+    case 'M':
+      flag_major = atoi(optarg);
+      break;
+    case 'm':
+      flag_minor = atoi(optarg);
+      break;
+    }
+
+  }
+
+  if (flag_create && flag_strip_partition) {
+    flag_help = 1;
+    warnx("-c and -d are incompatible at present.");
+    return;
+  }
+
+  if (optind < argc) {
+    flag_path = argv[optind++];
+  }
+
+  if (optind < argc) {
+    fprintf(stderr, "Too many free arguments: %d\n", argc - optind);
+    flag_help = 1;
+   }
+}
+
+int main(int argc, char **argv) {
+  struct stat path_stat;
+  char path[PATH_MAX];
+  int ret;
+  dev_t root_dev;
+  parse_args(argc, argv);
+
+  if (flag_help) {
+    print_help(argv[0]);
+    return 1;
+  }
+
+  if (flag_major || flag_minor) {
+    root_dev = makedev(flag_major, flag_minor);
+  } else {
+    /* Yields the containing dev_t in st_dev. */
+    if (stat(flag_path, &path_stat) != 0)
+      err(1, "Cannot stat(%s)", flag_path);
+    root_dev = path_stat.st_dev;
+  }
+
+  ret = rootdev_wrapper(path, sizeof(path),
+                        flag_use_slave,
+                        flag_strip_partition,
+                        &root_dev,
+                        flag_block_path,
+                        flag_dev_path);
+
+  if (ret == 1 && flag_create) {
+    /* TODO(wad) add flag_force to allow replacement */
+    ret = 0;
+    if (mknod(path, S_IFBLK | S_IRUSR | S_IWUSR, root_dev) && errno != EEXIST) {
+      warn("failed to create %s", path);
+      ret = 1;
+    }
+  }
+
+  if (flag_ignore && ret > 0)
+    ret = 0;
+
+  if (path[0] != '\0')
+    printf("%s\n", path);
+
+  return ret;
+}
diff --git a/rootdev.c b/rootdev.c
index c3dc175..867974f 100644
--- a/rootdev.c
+++ b/rootdev.c
@@ -1,100 +1,389 @@
-/* Taken from util-linux source. GPLv2.
- * Emits the current rootfs device.
- * Works by searching /dev recursively for a BLK device with the same device
- * number as '/'.
+/* Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ *
+ * Implements root device discovery via sysfs with optional bells and whistles.
  */
 
-#include <stdio.h>
-#include <err.h>
-#include <sys/types.h>
+#include "rootdev.h"
+
+#include <ctype.h>
 #include <dirent.h>
-#include <sys/stat.h>
+#include <err.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+static const char *kDefaultSearchPath = "/sys/block";
+static const char *kDefaultDevPath = "/dev";
+
+/* Encode the root device structuring here for Chromium OS */
+static const char kActiveRoot[] = "/dev/ACTIVE_ROOT";
+static const char kRootDev[] = "/dev/ROOT";
+static const char kRootA[] = "/dev/ROOT0";
+static const char kRootB[] = "/dev/ROOT1";
+
+struct part_config {
+  const char *name;
+  int offset;
+};
+
+#define CHROMEOS_PRIMARY_PARTITION 3
+static const struct part_config kPrimaryPart[] = { { kRootA,    0 },
+                                                   { kRootDev, -3 },
+                                                   { kRootB,    2 } };
+#define CHROMEOS_SECONDARY_PARTITION 5
+static const struct part_config kSecondaryPart[] = { { kRootB,    0 },
+                                                     { kRootDev, -5 },
+                                                     { kRootA,   -2 } };
+
+/* The number of entries in a part_config so we could add RootC easily. */
+static const int kPartitionEntries = 3;
+
+/* Converts a file of %u:%u -> dev_t. */
+static dev_t devt_from_file(const char *file) {
+  char candidate[10];  /* TODO(wad) system-provided constant? */
+  ssize_t bytes = 0;
+  unsigned int major = 0;
+  unsigned int minor = 0;
+  dev_t dev = 0;
+  int fd = -1;
+
+  /* Never hang. Either get the data or return 0. */
+  fd = open(file, O_NONBLOCK | O_RDONLY);
+  if (fd < 0)
+    return 0;
+  bytes = read(fd, candidate, sizeof(candidate));
+  close(fd);
+
+  /* 0:0 should be considered the minimum size. */
+  if (bytes < 3)
+    return 0;
+  candidate[bytes] = 0;
+  if (sscanf(candidate, "%u:%u", &major, &minor) == 2) {
+    /* candidate's size artificially limits the size of the converted
+     * %u to safely convert to a signed int. */
+    dev = makedev(major, minor);
+  }
+  return dev;
+}
+
+/* Walks sysfs and will recurse into any directory/link that represents
+ * a block device to find sub-devices (partitions).
+ * If dev == 0, the first device in the directory will be returned. */
+static int match_sysfs_device(char *name, size_t name_len,
+                              const char *basedir, dev_t *dev) {
+  int found = -1;
+  size_t basedir_len;
+  DIR *dirp = NULL;
+  struct dirent *entry = NULL;
+  struct dirent *next = NULL;
+  char *working_path = NULL;
+  long working_path_size = 0;
+
+  if (!name || !name_len || !basedir || !dev) {
+    warnx("match_sysfs_device: invalid arguments supplied");
+    return -1;
+  }
+  basedir_len = strlen(basedir);
+  if (!basedir_len) {
+    warnx("match_sysfs_device: basedir must not be empty");
+    return -1;
+  }
+
+  errno = 0;
+  dirp = opendir(basedir);
+  if (!dirp) {
+     /* Don't complain if the directory doesn't exist. */
+     if (errno != ENOENT)
+       warn("match_sysfs_device:opendir(%s)", basedir);
+     return found;
+  }
+
+  /* Grab a platform appropriate path to work with.
+   * Ideally, this won't vary under sys/block. */
+  working_path_size = pathconf(basedir, _PC_NAME_MAX) + 1;
+  /* Fallback to PATH_MAX on any pathconf error. */
+  if (working_path_size < 0)
+    working_path_size = PATH_MAX;
+
+  working_path = malloc(working_path_size);
+  if (!working_path) {
+    warn("malloc(dirent)");
+    closedir(dirp);
+    return found;
+  }
+
+  /* Allocate a properly sized entry. */
+  entry = malloc(offsetof(struct dirent, d_name) + working_path_size);
+  if (!entry) {
+    warn("malloc(dirent)");
+    free(working_path);
+    closedir(dirp);
+    return found;
+  }
+
+  while (readdir_r(dirp, entry, &next) == 0 && next) {
+    size_t candidate_len = strlen(entry->d_name);
+    size_t path_len = 0;
+    dev_t found_devt = 0;
+    /* Ignore the usual */
+    if (!strcmp(entry->d_name, ".") || !strcmp(entry->d_name, ".."))
+      continue;
+    /* TODO(wad) determine how to best bubble up this case. */
+    if (candidate_len > name_len)
+      continue;
+    /* Only traverse directories or symlinks (to directories ideally) */
+    switch (entry->d_type) {
+    case DT_UNKNOWN:
+    case DT_DIR:
+    case DT_LNK:
+      break;
+    default:
+      continue;
+    }
+    /* Determine path to block device number */
+    path_len = snprintf(working_path, working_path_size, "%s/%s/dev",
+                        basedir, entry->d_name);
+    /* Ignore if truncation occurs. */
+    if (path_len != candidate_len + basedir_len + 5)
+      continue;
+
+    found_devt = devt_from_file(working_path);
+    /* *dev == 0 is a wildcard. */
+    if (!*dev || found_devt == *dev) {
+      snprintf(name, name_len, "%s", entry->d_name);
+      *dev = found_devt;
+      found = 1;
+      break;
+    }
+
+    /* Recurse one level for devices that may have a matching partition. */
+    if (major(found_devt) == major(*dev) && minor(*dev) > minor(found_devt)) {
+      sprintf(working_path, "%s/%s", basedir, entry->d_name);
+      found = match_sysfs_device(name, name_len, working_path, dev);
+      if (found > 0)
+        break;
+    }
+  }
+
+  free(working_path);
+  free(entry);
+  closedir(dirp);
+  return found;
+}
+
+const char *rootdev_get_partition(const char *dst, size_t len) {
+  const char *end = dst + strnlen(dst, len);
+  const char *part = end - 1;
+  if (!len)
+    return NULL;
+
+  if (!isdigit(*part--))
+    return NULL;
+
+  while (part > dst && isdigit(*part)) part--;
+  part++;
+
+  if (part >= end)
+    return NULL;
+
+  return part;
+}
+
+void rootdev_strip_partition(char *dst, size_t len) {
+  char *part = (char *)rootdev_get_partition(dst, len);
+  if (!part)
+    return;
+  /* For devices that end with a digit, the kernel uses a 'p'
+   * as a separator. E.g., mmcblk1p2. */
+  if (*(part - 1) == 'p')
+    part--;
+  *part = '\0';
+}
+
+int rootdev_symlink_active(const char *path) {
+  int ret = 0;
+  /* Don't overwrite an existing link. */
+  errno = 0;
+  if ((symlink(path, kActiveRoot)) && errno != EEXIST) {
+    warn("failed to symlink %s -> %s", kActiveRoot, path);
+    ret = -1;
+  }
+  return ret;
+}
+
+int rootdev_get_device(char *dst, size_t size, dev_t dev,
+                       const char *search) {
+  struct stat active_root_statbuf;
+
+  if (search == NULL)
+    search = kDefaultSearchPath;
+
+  /* Check if the -s symlink exists. */
+  if ((stat(kActiveRoot, &active_root_statbuf) == 0) &&
+      active_root_statbuf.st_rdev == dev) {
+    /* Note, if the link is not fully qualified, this won't be
+     * either. */
+    ssize_t len = readlink(kActiveRoot, dst, PATH_MAX);
+    if (len > 0) {
+      dst[len] = 0;
+      return 0;
+    }
+    /* If readlink fails or is empty, fall through */
+  }
+
+  snprintf(dst, size, "%s", search);
+  if (match_sysfs_device(dst, size, dst, &dev) <= 0) {
+    fprintf (stderr, "unable to find match\n");
+    return 1;
+  }
+
+  return 0;
+}
+
+int rootdev_get_device_slave(char *slave, size_t size, dev_t *dev,
+                             const char *device, const char *search) {
+  char dst[PATH_MAX];
+  int len = 0;
+
+  if (search == NULL)
+    search = kDefaultSearchPath;
+
+  /* So far, I've only seen top-level block devices with slaves. */
+  len = snprintf(dst, sizeof(dst), "%s/%s/slaves", search, device);
+  if (len < 0 || len != strlen(device) + strlen(search) + 8) {
+    warnx("rootdev_get_device_slave: device name too long");
+    return -1;
+  }
+  *dev = 0;
+  if (match_sysfs_device(slave, size, dst, dev) <= 0)
+    return -1;
+
+  return 0;
+}
+
+int rootdev_create_devices(const char *name, dev_t dev, bool symlink) {
+  int ret = 0;
+  unsigned int major = major(dev);
+  unsigned int minor = minor(dev);
+  int i;
+  const struct part_config *config;
+  const char *part_s = rootdev_get_partition(name, strlen(name));
 
+  if (part_s == NULL) {
+    warnx("create_devices: unable to determine partition");
+    return -1;
+  }
 
-static int
-find_dev_recursive(char *dirnamebuf, int number, int deviceOnly) {
-        DIR *dp;
-        struct dirent *dir;
-        struct stat s;
-        int dirnamelen = 0;
-
-        if ((dp = opendir(dirnamebuf)) == NULL)
-                err(1, "can't read directory %s", dirnamebuf);
-        dirnamelen = strlen(dirnamebuf);
-        while ((dir = readdir(dp)) != NULL) {
-                if (!strcmp(dir->d_name, ".") || !strcmp(dir->d_name, ".."))
-                        continue;
-                if (dirnamelen + 1 + strlen(dir->d_name) > PATH_MAX)
-                        continue;
-                dirnamebuf[dirnamelen] = '/';
-                strcpy(dirnamebuf+dirnamelen+1, dir->d_name);
-                if (lstat(dirnamebuf, &s) < 0)
-                        continue;
-                if ((s.st_mode & S_IFMT) == S_IFBLK && s.st_rdev == number){
-                        if (deviceOnly) {
-                                int len = strlen(dirnamebuf);
-                                char c = 0;
-                                do {
-                                        c = dirnamebuf[len-1];
-                                        --len;
-                                }while(c > 0 && c < 9 && len > 0);
-                                /* arm has "p" for partition */
-                                if (dirnamebuf[len-1] == 'p')
-                                        --len;
-                                dirnamebuf[len]='\0';
-                        }
-                        return 1;
-                }
-                if ((s.st_mode & S_IFMT) == S_IFDIR &&
-                    find_dev_recursive(dirnamebuf, number, deviceOnly))
-                        return 1;
-        }
-        dirnamebuf[dirnamelen] = 0;
-        closedir(dp);
-        return 0;
+  switch (atoi(part_s)) {
+  case CHROMEOS_PRIMARY_PARTITION:
+    config = kPrimaryPart;
+    break;
+  case CHROMEOS_SECONDARY_PARTITION:
+    config = kSecondaryPart;
+    break;
+  default:
+    warnx("create_devices: unable to determine partition: %s",
+          part_s);
+    return -1;
+  }
+
+  for (i = 0; i < kPartitionEntries; ++i) {
+    dev = makedev(major, minor + config[i].offset);
+    errno = 0;
+    if (mknod(config[i].name,
+              S_IFBLK | S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH,
+              dev) && errno != EEXIST) {
+      warn("failed to create %s", config[i].name);
+      return -1;
+    }
+  }
+
+  if (symlink)
+    ret = rootdev_symlink_active(config[0].name);
+  return ret;
 }
 
-void usage(){
-   printf ("rootdev \n\t-d (for device only)\n");
+int rootdev_get_path(char *path, size_t size, const char *device,
+                     dev_t dev, const char *dev_path) {
+  int path_len;
+  struct stat dev_statbuf;
+
+  if (!dev_path)
+    dev_path = kDefaultDevPath;
+
+  if (!path || !size || !device)
+    return -1;
+
+  path_len = snprintf(path, size, "%s/%s", dev_path, device);
+  if (path_len != strlen(dev_path) + 1 + strlen(device))
+    return -1;
+
+  if (stat(path, &dev_statbuf) != 0)
+    return 1;
+
+  if (dev && dev != dev_statbuf.st_rdev)
+    return 2;
+
+  return 0;
 }
 
-int main(int argc, char *argv[]) {
-        struct stat s;
-        char *file = "/";
-        static char name[PATH_MAX+1];
-        int deviceOnly=0;
-        int c;
-        extern char *optarg;
-        extern int optind, optopt;
-        while ((c = getopt(argc, argv, "hd")) != -1) {
-                switch(c) {
-                case 'd':
-                        deviceOnly=1;
-                        break;
-                case 'h':
-                default:
-                        usage();
-                        return 1;
-                }
-        }
-        if (argc - optind >= 1)
-                file = argv[optind];
-
-        if (stat(file, &s) < 0)
-                err(1, "unable to stat %s", file);
-
-        if (!s.st_dev)
-                err(1, "unknown device number 0");
-
-        strcpy(name, "/dev");
-
-        if (!find_dev_recursive(name, s.st_dev, deviceOnly)) {
-                fprintf(stderr, "unable to find match\n");
-                return 1;
-        }
-
-        printf("%s\n", name);
-
-        return 0;
+int rootdev_wrapper(char *path, size_t size,
+                    bool full, bool strip,
+                    dev_t *dev,
+                    const char *search, const char *dev_path) {
+  int res = 0;
+  char devname[PATH_MAX];
+  if (!search)
+    search = kDefaultSearchPath;
+  if (!dev_path)
+   dev_path = kDefaultDevPath;
+  if (!dev)
+    return -1;
+
+  res = rootdev_get_device(devname, sizeof(devname), *dev, search);
+  if (res != 0)
+    return res;
+
+  if (full)
+    res = rootdev_get_device_slave(devname, sizeof(devname), dev, devname,
+                                   search);
+
+  /* TODO(wad) we should really just track the block dev, partition number, and
+   *           dev path.  When we rewrite this, we can track all the sysfs info
+   *           in the class. */
+  if (strip) {
+    /* When we strip the partition, we don't want get_path to return non-zero
+     * because of dev mismatch.  Passing in 0 tells it to not test. */
+    *dev = 0;
+    rootdev_strip_partition(devname, size);
+  }
+
+  res = rootdev_get_path(path, size, devname, *dev, dev_path);
+
+  return res;
+}
+
+int rootdev(char *path, size_t size, bool full, bool strip) {
+  struct stat root_statbuf;
+
+  /* Yields the containing dev_t in st_dev. */
+  if (stat("/", &root_statbuf) != 0)
+    return -1;
+
+  return rootdev_wrapper(path,
+                         size,
+                         full,
+                         strip,
+                         &root_statbuf.st_dev,
+                         NULL,  /* default /sys dir */
+                         NULL);  /* default /dev dir */
 }
diff --git a/rootdev.h b/rootdev.h
new file mode 100644
index 0000000..03b8bd8
--- /dev/null
+++ b/rootdev.h
@@ -0,0 +1,104 @@
+/* Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ *
+ * Interface for root device discovery via sysfs with optional
+ * bells and whistles.
+ */
+#ifndef ROOTDEV_ROOTDEV_H_
+#define ROOTDEV_ROOTDEV_H_
+
+#include <stdbool.h>
+#include <sys/types.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * rootdev: returns the path to the root device in @path
+ * @path: pre-allocated char array the result will be written to
+ * @size: size of @path
+ * @full: whether to try to do full resolution. E.g., device-mapper
+ * @strip: whether to remove the partition # or not.
+ *
+ * Returns 0 on success, non-zero on error.
+ */
+int rootdev(char *path, size_t size, bool full, bool strip);
+
+/* All interface below this point will most definitely be C specific. If
+ * we rewrite this as a C++ class, only the above generic interface should
+ * still be provided.
+ */
+
+/**
+ * rootdev_wrapper: rootdev equivalent with paths can be substituted.
+ */
+int rootdev_wrapper(char *path, size_t size,
+                    bool full, bool strip,
+                    dev_t *dev,
+                    const char *search, const char *dev_path);
+/**
+ * rootdev_get_device: finds the /dev path for @dev
+ * @dst: destination char array
+ * @size: size of @dst
+ * @dev: dev_t specifying the known root device
+ * @search: path to search under. NULL for default.
+ *
+ * Returns 0 on success, non-zero on error.
+ *
+ * The name of the devices is placed in @dst. It will not
+ * be qualified with /dev/ by default.
+ */
+int rootdev_get_device(char *dst, size_t size, dev_t dev,
+                       const char *search);
+
+/**
+ * rootdev_get_device_slave: returns the first device under @device/slaves
+ * @slave: destination char array for storing the result
+ * @size: size of @slave
+ * @dev: pointer to a dev_t to populate
+ * @device: name of the device to probe, like "sdb"
+ * @search: path to search under. NULL for default.
+ *
+ * Returns 0 on success, non-zero on failure.
+ * It is safe for @device == @slave.
+ */
+int rootdev_get_device_slave(char *slave, size_t size, dev_t *dev,
+                             const char *device, const char *search);
+
+/**
+ * rootdev_get_path: converts a device name to a path in the device tree
+ * @path: char array to store the path
+ * @size: size of @devpath
+ * @device: name of the device
+ * @dev: optional expected dev_t of the node.
+ * @dev_path: path to dev tree. NULL for default (/dev)
+ *
+ * A @dev of 0 is ignored.
+ *
+ * @path is populated for all return codes.
+ * Returns 0 on success and non-zero on error:
+ * -1 on unexpected errors (@path may be invalid)
+ *  1 on no existing @path
+ *  2 @path exists but the dev_t value is mismatched.
+ *
+ * Nb, this function does NOT search /dev for a match.  It performs a normal
+ *     string concatenation and probes for the existence.  If udev has moved,
+ *     or otherwise renamed, the device, a positive value is returned.
+ *     The caller may then use the dev_t and @path to create the node with
+ *     mknod(2).
+ */
+int rootdev_get_path(char *path, size_t size, const char *device, dev_t dev,
+                     const char *dev_path);
+
+const char *rootdev_get_partition(const char *dst, size_t len);
+void rootdev_strip_partition(char *dst, size_t len);
+int rootdev_symlink_active(const char *path);
+int rootdev_create_devices(const char *name, dev_t dev, bool symlink);
+
+#ifdef __cplusplus
+}  /* extern "C" */
+#endif
+
+#endif  /* ROOTDEV_ROOTDEV_H_ */
diff --git a/rootdev_test.sh b/rootdev_test.sh
new file mode 100755
index 0000000..8c188c3
--- /dev/null
+++ b/rootdev_test.sh
@@ -0,0 +1,291 @@
+#!/bin/sh
+# Copyright (C) 2010 The Chromium OS Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+#
+# Simple functional test harness for rootdev
+# TODO(wad) rootdev should be rewritten in C++ and gmocked.
+
+set -u
+
+warn () {
+  echo "WARN: $@" 1>&2
+}
+
+error () {
+  echo "ERROR: $@" 1>&2
+  exit 1
+}
+
+PASS_COUNT=0
+pass () {
+  echo "PASS:$1" 1>&2
+  PASS_COUNT=$((PASS_COUNT + 1))
+  return 0
+}
+
+FAIL_COUNT=0
+fail () {
+  echo "FAIL:$1" 1>&2
+  FAIL_COUNT=$((FAIL_COUNT + 1))
+  return 0
+}
+
+WORKDIR=
+cleanup () {
+  if [ -n "$WORKDIR" ]; then
+    rm -rf "$WORKDIR"
+  fi
+  trap - EXIT
+}
+
+setup () {
+  WORKDIR=$(mktemp -d rootdev_test.XXXXXXX)
+  if [ ! -d "$WORKDIR" ]; then
+    error "Failed to create temporary work dir"
+  fi
+  trap cleanup EXIT
+}
+
+run_test () {
+  setup
+  echo "RUN:$1" 1>&2
+  eval $1
+  ret=$?
+  cleanup
+  if [ $ret -eq 0 ]; then
+    pass $1
+  else
+    fail $1
+  fi
+}
+
+expect () {
+  cond="$1"
+  eval test $1
+  if [ $? -ne 0 ]; then
+    warn "expect: $1"
+    return 1
+  fi
+  return 0
+}
+
+if [ ! -e ./rootdev ]; then
+  error "rootdev must be in the cwd"
+fi
+
+if [ "$USER" != "root" ]; then
+  error "Must be run as root to use mknod ($USER)"
+fi
+
+t00_bad_sys_dir () {
+  out=$(./rootdev --block $WORKDIR 2>/dev/null)
+  expect "$? -ne 0" || return 1
+  expect "-z '$out'" || return 1
+}
+run_test t00_bad_sys_dir
+
+h00_setup_sda_tree() {
+  local block=$1
+  local dev=$2
+  mkdir -p $block
+  mkdir -p $dev
+  mkdir -p $block/sda/sda1
+  mkdir -p $block/sda/sda2
+  echo "10:0" > $block/sda/dev
+  echo "10:1" > $block/sda/sda1/dev
+  echo "10:2" > $block/sda/sda2/dev
+  mknod $dev/sda1 b 10 1
+  mknod $dev/sda2 b 10 2
+  mknod $dev/sda b 10 0
+}
+
+t01_sys_dev_match () {
+  local block=$WORKDIR/sys/block
+  local dev=$WORKDIR/dev
+  h00_setup_sda_tree $block $dev
+
+  out=$(./rootdev --dev $dev --block $block --major 10 --minor 1 2>/dev/null)
+  expect "$? -eq 0" || return 1
+  expect "'$dev/sda1' = '$out'" || return 1
+}
+run_test t01_sys_dev_match
+
+t02_sys_dev_match_block () {
+  local block=$WORKDIR/sys/block
+  local dev=$WORKDIR/dev
+  h00_setup_sda_tree $block $dev
+
+  out=$(./rootdev --dev $dev --block $block --major 10 --minor 0 2>/dev/null)
+  expect "$? -eq 0" || return 1
+  expect "'$dev/sda' = '$out'" || return 1
+}
+run_test t02_sys_dev_match_block
+
+t03_sys_dev_match_block_no_dev () {
+  local block=$WORKDIR/sys/block
+  local dev=$WORKDIR/dev
+  h00_setup_sda_tree $block $dev
+  rm $dev/sda
+
+  out=$(./rootdev --dev $dev --block $block --major 10 --minor 0 2>/dev/null)
+  expect "$? -eq 1" || return 1
+  expect "'$dev/sda' = '$out'" || return 1
+}
+run_test t03_sys_dev_match_block_no_dev
+
+t04_sys_dev_match_block_no_dev_ignore () {
+  local block=$WORKDIR/sys/block
+  local dev=$WORKDIR/dev
+  h00_setup_sda_tree $block $dev
+  rm $dev/sda
+
+  out=$(./rootdev -i --dev $dev --block $block --major 10 --minor 0 2>/dev/null)
+  expect "$? -eq 0" || return 1
+  expect "'$dev/sda' = '$out'" || return 1
+}
+run_test t04_sys_dev_match_block_no_dev_ignore
+
+
+h01_setup_dm_tree() {
+  local block=$1
+  local dev=$2
+  mkdir -p $block
+  mkdir -p $dev
+  mkdir -p $block/dm-0
+  mkdir -p $block/dm-0/slaves/sda1
+  echo "254:0" > $block/dm-0/dev
+  echo "10:1" > $block/dm-0/slaves/sda1/dev
+  mknod $dev/dm-0 b 254 0
+}
+
+t05_match_dm () {
+  local block=$WORKDIR/sys/block
+  local dev=$WORKDIR/dev
+  h00_setup_sda_tree $block $dev
+  h01_setup_dm_tree $block $dev
+
+  out=$(./rootdev --dev $dev --block $block --major 254 --minor 0 \
+        2>/dev/null)
+  expect "$? -eq 0" || return 1
+  expect "'$dev/dm-0' = '$out'" || return 1
+}
+run_test t05_match_dm
+
+t06_match_dm_slave () {
+  local block=$WORKDIR/sys/block
+  local dev=$WORKDIR/dev
+  h00_setup_sda_tree $block $dev
+  h01_setup_dm_tree $block $dev
+
+  out=$(./rootdev -s --dev $dev --block $block --major 254 --minor 0 \
+        2>/dev/null)
+  expect "$? -eq 0" || return 1
+  expect "'$dev/sda1' = '$out'" || return 1
+}
+run_test t06_match_dm_slave
+
+t07_safe_fail_on_no_slave () {
+  local block=$WORKDIR/sys/block
+  local dev=$WORKDIR/dev
+  h00_setup_sda_tree $block $dev
+  h01_setup_dm_tree $block $dev
+
+  out=$(./rootdev -s --dev $dev --block $block --major 10 --minor 1 \
+        2>/dev/null)
+  expect "$? -eq 0" || return 1
+  expect "'$dev/sda1' = '$out'" || return 1
+}
+run_test t07_safe_fail_on_no_slave
+
+t08_safe_fail_on_no_slave_dev () {
+  local block=$WORKDIR/sys/block
+  local dev=$WORKDIR/dev
+  h00_setup_sda_tree $block $dev
+  h01_setup_dm_tree $block $dev
+  # If the matching dev node is missing, an error code will be returned
+  # but the path will still represent the slave.
+  rm $dev/sda1
+
+  out=$(./rootdev -s --dev $dev --block $block --major 254 --minor 0 \
+        2>/dev/null)
+  expect "$? -eq 1" || return 1
+  expect "'$dev/sda1' = '$out'" || return 1
+}
+run_test t08_safe_fail_on_no_slave_dev
+
+t09_safe_fail_on_no_slave_dev_ignore () {
+  local block=$WORKDIR/sys/block
+  local dev=$WORKDIR/dev
+  h00_setup_sda_tree $block $dev
+  h01_setup_dm_tree $block $dev
+  # If the matching dev node is missing, an error code will be returned
+  # but the path will still represent the slave.
+  rm $dev/sda1
+
+  out=$(./rootdev -i -s --dev $dev --block $block --major 254 --minor 0 \
+        2>/dev/null)
+  expect "$? -eq 0" || return 1
+  expect "'$dev/sda1' = '$out'" || return 1
+}
+run_test t09_safe_fail_on_no_slave_dev_ignore
+
+h02_setup_mmc_tree() {
+  local block=$1
+  local dev=$2
+  mkdir -p $block
+  mkdir -p $dev
+  mkdir -p $block/mmcblk0/mmcblk0p1
+  mkdir -p $block/mmcblk0/mmcblk0p2
+  echo "11:0" > $block/mmcblk0/dev
+  echo "11:1" > $block/mmcblk0/mmcblk0p1/dev
+  echo "11:2" > $block/mmcblk0/mmcblk0p2/dev
+  mknod $dev/mmcblk0 b 11 0
+  mknod $dev/mmcblk0p1 b 11 1
+  mknod $dev/mmcblk0p2 b 11 2
+}
+
+t10_mmcdev () {
+  local block=$WORKDIR/sys/block
+  local dev=$WORKDIR/dev
+  h02_setup_mmc_tree $block $dev
+  out=$(./rootdev --dev $dev --block $block --major 11 --minor 2 \
+        2>/dev/null)
+  expect "$? -eq 0" || return 1
+  expect "'$dev/mmcblk0p2' = '$out'" || return 1
+}
+run_test t10_mmcdev
+
+t11_mmcdev_strip () {
+  local block=$WORKDIR/sys/block
+  local dev=$WORKDIR/dev
+  h02_setup_mmc_tree $block $dev
+  out=$(./rootdev -d --dev $dev --block $block --major 11 --minor 2 \
+        2>/dev/null)
+  expect "$? -eq 0" || return 1
+  expect "'$dev/mmcblk0' = '$out'" || return 1
+}
+run_test t11_mmcdev_strip
+
+t12_sda_strip () {
+  local block=$WORKDIR/sys/block
+  local dev=$WORKDIR/dev
+  h00_setup_sda_tree $block $dev
+  out=$(./rootdev -d --dev $dev --block $block --major 10 --minor 2 \
+        2>/dev/null)
+  expect "$? -eq 0" || return 1
+  expect "'$dev/sda' = '$out'" || return 1
+}
+run_test t12_sda_strip
+
+# TODO(wad) add node creation tests
+
+TEST_COUNT=$((PASS_COUNT + FAIL_COUNT))
+
+echo "----"
+echo "Test passed:  $PASS_COUNT / $TEST_COUNT"
+echo "Test failed:  $FAIL_COUNT / $TEST_COUNT"
+
+if [ $FAIL_COUNT -ne 0 ]; then
+  exit 1
+fi